1. Field of the Invention
This invention relates to a lens shutter for cameras provided with a light-amount control means which is capable of limiting the amount of light from an object, reaching a film or a CCD, for example, by restricting the diameter of an exposure aperture.
2. Description of Related Art
As is well known, shutters for cameras are divided into two types: a lens shutter located close to a photographic lens and a focal-plane shutter located immediately before a film or a CCD. The lens shutter is such that a circular exposure aperture is opened and closed, and in general, the exposure aperture is opened from the center thereof and closed toward the center by a plurality of shutter blades. However, a lens shutter having a single shutter blade is also available in which the exposure aperture is opened from a predetermined periphery thereof and closed toward the periphery after fully opened.
On the other hand, a camera generally has a light-amount control mechanism placed close to a photographic lens. Such light-amount control mechanisms commonly used are called diaphragm mechanisms, which are of two main types. One is constructed so that a plurality of stop blades are rotated simultaneously in the same direction or operated (including rotation) simultaneously in an opposite direction, and the diameter of the aperture can be continuously changed, with the optical axis as a center, by the cooperation of these blades. The other is such that, by providing a stop member with at least one circular aperture which is smaller in diameter than the exposure aperture or a plurality of stop members with a single aperture, the aperture can be selectively introduced into a photographing optical path.
In addition to the diaphragm mechanisms, mechanisms using ND filters are available for the light-amount control mechanisms. In this case, there are those in which one ND filter having a predetermined density is introduced into the exposure aperture and those in which a plurality of ND filters different in density are provided and selectively introduced into the exposure aperture. In the mechanisms using the ND filters, there are those combined with the diaphragm mechanisms of the latter type, of the diaphragm mechanisms of the above two types. As an example, a circular aperture smaller in diameter than the exposure aperture is covered with the ND filter, and this covered aperture is introduced into the exposure aperture. Such a light-amount control mechanism is suitable for the case where it is desirable that the influence of diffraction is excluded because the amount of light from the object can be materially reduced without extremely diminishing the aperture.
As will be seen from the above description, the lens shutter mechanism and the light-amount control mechanism are not located immediately before the film or the CCD, but close to the photographic lens. Thus, in a camera provided with these two mechanisms, it has been common practice to manufacture the two mechanisms as one unit. An example of this case is set forth in Japanese Patent Kokai No. 2001-117135.
As is well known, in the case where only the lens shutter mechanism is unified, the mechanism has been constructed so that shutter blades are operated in a blade chamber provided between two plate members. Even where only the light-amount control mechanism is unified, stop blades are operated in the blade chamber provided between the two plate members. In the case where the two mechanisms are simply unified, therefore, two chambers must be provided by four plate members. However, this structure is unfavorable for a low cost and a reduction in thickness (a diminution in dimension in a direction along the optical axis) of the unit. Consequently, as set forth in the above publication, it has been common practice to provide two chambers by three plate members.
Units of this type have been used in compact cameras, and most of them have been motorized. With a rapid development in digital cameras, demands for cost reduction and compactness of such a unit have recently been further increased. In particular, the unit of this type is placed in the proximity of the photographic lens, and thus a reduction in thickness of a circular region, with the optical axis adjacent to the photographic lens as a center, is greatly required.
It is, therefore, an object of the present invention to provide a lens shutter for cameras which is suitable for compactness, designed so that, at least, the thickness of an area immediately the photographic lens is reduced, irrespective of the integration of the shutter mechanism and the light-amount control mechanism which are operated by individual motors.
In order to achieve the above object, the lens shutter for cameras of the present invention includes two base plates in which a blade chamber is provided between them and their apertures are superposed to provide a circular exposure aperture, at least one shutter blade located in the blade chamber to perform the opening and closing operation of the exposure aperture, a first motor mounted to one of the base plates outside the blade chamber so that an output port extends to the blade chamber to cause the shutter blade to perform the opening and closing operation, a light-amount control means located in the blade chamber to perform the introducing and removing operations with respect to the exposure aperture, and a second motor mounted to one of the base plates outside the blade chamber so that an output port extends to the blade chamber to cause the light-amount control means to perform the introducing and removing operations. In this case, the light-mount control means is located so that a part thereof always overlaps the shutter blade adjacent thereto in any operating condition.
In the lens shutter for cameras of the present invention, the light-amount control means may have an aperture smaller in diameter than the exposure aperture so that the aperture is introduced into, and removed from, the exposure aperture. In this case, when the aperture of the light-amount control means is covered with the sheet of the ND filter, light from the object can be further attenuated.
In the lens shutter for cameras of the present invention, the light-amount control means is constructed with a first member having an aperture smaller in diameter than the exposure aperture and a second member having only the function of blocking light. Where the aperture of the first member is introduced into the exposure aperture, a gap is provided between the first member and the edge of the exposure aperture. When the gap is covered with the second member, the contour of each of the base plates can be diminished. In this case also, when the aperture of the first member is covered with the sheet of the ND filter, the light from the object can be further attenuated.
In the lens shutter for cameras of the present invention, the light-amount control means may be constructed with two stop blades which are relatively rotated so that the area of the exposure aperture can be limited by these two stop blades.
In the lens shutter for cameras of the present invention, the light-amount control means may be constructed with a sheet material of the ND filter.
This and other objects as well as the features and advantages of the present invention will become apparent from the following detailed description of the preferred embodiments when taken in conjunction with the accompanying drawings.